Although the eye contains three types of cone: long-wavelength-sensitive (L), medium-wavelength-sensitive (M), and short-wavelength-sensitive (S), the L and M cones comprise over 90% of our cones. In the fovea, the portion of the retina used for high acuity tasks such as reading, the L:M cone ratio varies tremendously across people, even among people with normal color vision. The cause of this variability is presently unknown, however evidence suggests that one source of this variation is inherent to the genetic mechanisms that determine which gene, L or M, from the X-chromosome visual pigment gene array a photoreceptor chooses to express. For this project, I propose to test the hypothesis that DNA sequence variation at the X chromosome visual pigment gene locus plays a role in determining the L:M cone ratio. Regions of the L/M pigment gene array will be sequenced in DNA from subjects with known L:M cone ratios. Sequence differences will be analyzed for correlation with cone ratio. Understanding how the retina is formed not only clarifies color vision, but also advances our understanding of retinal malformations and degeneration. [unreadable] [unreadable]